A feed device for feeding chips and short-cut fibers into an extruder for producing fiber-reinforced plastics materials is known from DE 102 01 869 A1. The feeding takes place by a mixer by means of a two-screw auxiliary extruder, which opens laterally into the extruder and conveys the short-cut fibers into the extruder. The short-cut fibers are sucked via a downpipe and a mixer by means of an airstream into the auxiliary extruder. For this purpose, a fan, which produces the fiber airstream, opens below the screw shafts into the housing of the auxiliary extruder. The fiber airstream is separated by a screen, the air being sucked out of the housing of the auxiliary extruder. To clean the screen, compressed air is fed below said screen via a line, the line being closable in the direction of the fan by the fed compressed air by means of a check valve.